Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilitating or fatal to domestic animals, and may also affect humans. Ticks are especially important to domestic animals in tropical and subtropical countries, where the warm climate enables many species to flourish. Also, the large populations of wild animals in warm countries provide a reservoir of ticks and infective microbes that spread to domestic animals. Farmers of livestock animals use many methods to control ticks, and related treatments are used to reduce infestation of companion animals.
Variety of ticks affecting domestic animals
Ticks are invertebrate animals in the phylum Arthropoda, and are related to spiders. Ticks are in the subclass Acari, which consists of many orders of mites and one tick order, the Ixodida. Some mites are parasitic, but all ticks are parasitic feeders. Ticks pierce the skin of their hosts with specialized mouthparts to suck blood, and they survive exclusively by this obligate method of feeding. Some species of mites may be mistaken for larval ticks at infestations on animal hosts, but their feeding mechanisms are distinctive. All ticks have an incomplete metamorphosis: after hatching from the egg, a series of similar stages (instars) develops from a six-legged larva, to eight-legged nymph, and then a sexually developed, eight-legged adult. Between each stage is a molt (ecdysis), which enables the developing tick to expand within a new external skeleton. Ticks are grouped in three families, of which two have genera of importance to domestic animals, as follows. The family Argasidae contains the important genera Argas, Ornithodoros, and Otobius. These genera are known as soft ticks because their outer body surfaces lack hard plates. The family Ixodidae contains 14 genera, including Amblyomma, Dermacentor, Haemaphysalis, Hyalomma, Ixodes, Margaropus, and Rhipicephalus. Also, the important boophilid ticks, formerly of the genus Boophilus, are now classified as a subgenus within the genus Rhipicephalus. These genera are known as hard ticks because their outer surfaces have hard plates. Within these genera are, very roughly, 100 species of importance to domestic animals. Some of these species are also important to humans. The only countries that do not have some kind of problem with ticks on domestic animals are those that are permanently cold. An outline classification of the Acari, including the two families of ticks of importance to domestic animals is in the article Mites of livestock.
Typical ticks of domestic animals
Amblyomma and Rhipicephalus ixodid ticks
Amblyomma species are widespread on domestic animals throughout tropical and subtropical regions. Typical Amblyomma species are: Amblyomma americanum, the lone star tick of the Southern and Eastern US; Am. cajennense, the Cayenne tick of South America and Southern US; Amblyomma variegatum, the bont tick of Africa and the Caribbean (see Gallery below for photograph of female and male). A typical Rhipicephalus species is Rhipicephalus sanguineus, the tropical dog tick, specialized to feed only on dogs. It is distributed globally throughout the warm countries, wherever humans with their dogs live. Typical Rhipicephalus species that feed on cattle in Africa are R. appendiculatus, the brown ear-tick, and R. evertsi, the red-legged tick. Rhipicephalus (Boophilus) microplus (or now simply Rhipicephalus microplus) is the most important tick of cattle in many tropical and subtropical countries to which it spread from Southeast Asia on transported cattle.
Boophilid ticks, a subgenus within Rhipicephalus
These ticks, commonly known as cattle ticks or blue ticks, have a highly characteristic morphology and one-host lifecycle. They have high specificity for cattle as hosts and their morphological characteristics used for identification are less distinct than those of three-host rhipicephalids such as R. appendiculatus. They are economically important to the cattle-rearing industry by causing direct parasitic losses and by transmission of microbes. In addition to Rhipicephalus microplus, species of most importance to domestic animals are R. annulatus, which is widespread in tropical and subtropical countries, and R. decoloratus which occurs in Africa.
One-host lifecycle of R. microplus
These ticks are adapted to the advantages of specialising to feed on cattle and with all the feeding stages occurring on one individual host in a rapid sequence. They also can survive by feeding on deer or some wild bovid hosts. Infestation starts when larvae on vegetation attach to a new host. When a larva feeds, it molts at the site where it feeds and emerges as a nymph. The nymph feeds at the same site or close by and molts where it feeds. It emerges from molt as either an adult female or male. The female's single large blood meal is converted into a batch of 2000 eggs. The males take several small meals of blood to support their repeated attempts at mating. The molts are rapid and the next stage remains in the hair coat to start feeding again. The combined feeding and molting periods take about 21 days. The engorged female drops from the host, hides under leaf litter on soil surface, lays one batch of eggs, and then dies. When eggs hatch, the larvae crawl up grass stems and wait until they can attach to passing cattle.
Hyalomma ticks
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